Use the Page-Change-Class method to change the class of a top-level page.
Use the Property-Set method to change the class of an embedded page. Ordinarily, the Property-Set method requires that the source (of values) and the destination (to receive the values) be alike — assigning a string value into a string property, a page value into a page property, and so on.
However, you can establish the class of an embedded page using a special Property-Set syntax:
When the system executes this method, it sets the value of the pyObjClass property in the page to the string value. This changes the class of the page.